Preparation And Performance Of Two-dimension Ti₃C₂T_x Surface Modulation Anode Materials For Sodium Ion Battery

The rich resources of sodium-ion batteries are similar to those of lithium-ion batteries,making sodium-ion batteries have the potential to replace lithium-ion batteries.The two-dimensional material MXene has excellent electrochemical properties,a variety of adjustable surface functional groups and a unique two-dimensional structure,which makes it widely studied in sodium-ion battery anode materials.First-principles calculations show that the theoretical capacity of MXene is the highest when the surface of MXene is all oxygen functional group,followed by fluorine functional group and hydroxide functional group.Therefore,the regulation of the surface functional groups of oxygen-rich MXene has a significant effect on the capacity.However,it is difficult to prepare MXenes with single surface functional groups,and it is even more difficult to prepare MXene materials with single oxygen functional groups.The shortcoming of easy oxidation of MXene makes the preparation of multilayer MXene(Ti₃C₂T_x)with rich O-terminal groups more challenging.In view of the above shortcomings,the low melting boiling point of organic ascorbic acid(VC)was used to protect MXenes from oxidation during calcination in air,and oxygen-rich functional group MXene materials were prepared.The main research contents are as follows:(1)In this paper,It was that MXene(Ti₃C₂T_x)had been obtained by etching with HF acid solution.After,ascorbic acid(VC)and MXene were ground evenly in proportion and then calcined in muffle furnace.Bulk oxygen-rich MXene anode materials were prepared by a simple"hot melt decomposition"strategy.In the process of heat treatment,the gas generated by the decomposition of VC isolates Ti₃C₂T_x from the air,so that the Ti₃C₂T_x remains stable in the air.It was not be oxidized.The experimental results show that its oxidation resistance temperature can reach 300?.By studying the structure evolution of O-Ti₃C₂T_xand Ti₃C₂T_x electrodes during charging and discharging,this paper reveals the storage mechanism of sodium ions in O-Ti₃C₂T_x electrodes.The experimental results show that the bulk O-Ti₃C₂T_x evolves into active Ti₃C₂T_xnanoparticles during the cycle,while the bulk Ti₃C₂T_x forms amorphous matrix.In addition,the unique role of O-terminal group in stabilizing nanocrystals and the anti-aggregation effect of Na₁₆Ti₁₀O₂₈ nanocrystals generated at the edge of Ti₃C₂T_xnanoparticles contribute to the high sodium storage capacity of O-Ti₃C₂T_x materials.Though,at current densities as high as 1A/g,the O-Ti₃C₂T_x block electrode can provide a reversible capacity of 153 m Ah/g after 2500 cycles,demonstrating excellent sodium storage performance.(3)Based on the previous experimental exploration,in order to further reduce the F functional group on the surface,this paper firstly used 0.33M Na OH solution and MXene material to reduce the F content by water thermal reaction,and then calcined the MXene material after hydrothermal mixing with VC in proportion in muffle furnace at 300?.By comparison,it was found that the optimal mass ratio of the hydroheated MXene material to VC was changed,and the reversible specific capacity of 112 m Ah/g was obtained after 5000 cycles at the current density of 2 A/g.The experimental results show that the hydrothermal treatment has a great effect on the properties and capacity of MXene materials.